A GST return is a document containing details of all income & sales and or expenses & purchases that a GST-registered taxpayer every GSTIN is required to file with the tax administrative authorities. This is used by tax authorities to calculate net tax liability. Under the GST regime, regular businesses having more than Rs.5 crore as annual aggregate turnover and taxpayers who have not opted for the QRMP scheme have to file two monthly returns and one annual return. This amounts to 25 returns each year. 
Taxpayers with a turnover of up to Rs.5 crore have the option to file returns under the QRMP scheme. The number of GSTR filings for QRMP filers is 9 each year, which include 4 GSTR-1 and GSTR-3B returns each and an annual return. Note that QRMP filers have to pay tax on a monthly basis even though they are filing returns quarterly.
There are also separate statements & returns required to be filed in special cases such as composition dealers where the number of GSTR filings is 5 each year 4 statement-cum-challans in CMP-08 and 1 annual return GSTR-4.